Method for preparing silicon nitride ceramic with high strength and toughness

Abstract

Provided with a method for preparing a silicon nitride ceramic with high strength and toughness including: mixing 0.2-0.9 wt % of carbon (C) powder with silicon nitride powder containing 5.0-6.0 wt % of yttria (Y 2 O 3 ) and 1.0-2.0 wt % of alumina (Al 2 O 3 ) added thereto as a sintering agent, and preparing a molding; subjecting the molding to a carbothermal reduction treatment at 1400-1500° C.; and gas pressure sintering the molding at a temperature above 1850° C. after the carbothermal reduction treatment.

What is claimed is:  
     
       1. A method for preparing a silicon nitride ceramic with high strength and toughness comprising: 
       mixing 0.2-0.9 wt % of carbon (C) powder with silicon nitride powder containing 5.0-6.0 wt % of yttria (Y 2 O 3 ) and 1.0-2.0 wt % of alumina (Al 2 O 3 ) added thereto as a sintering agent, and preparing a molding;  
       subjecting the molding to a carbothermal reduction treatment at 1400-1500° C.; and  
       gas pressure sintering the molding at a temperature above 1850° C. after the carbothermal reduction treatment.  
     
     
       2. The method as claimed in claim  1 , wherein the molding after the carbothermal reduction treatment has a total oxygen content of 2.5-3.8 wt % and a remaining carbon content of less than 0.14 wt %. 
     
     
       3. The method as claimed in claim  1 , wherein the molding after the carbothermal reduction treatment has an oxynitride crystalline phase as a second phase.